1. Field of the Invention
The present invention is directed toward a type AC Armored Cable. More particularly, the present invention relates to a type AC THH armored cable assembly which includes electrical conductors each having a conventional layer of insulation, a jacketing layer and an extruded protective layer.
2. Discussion of Related Art
Armored cable (“AC”) and Metal-Clad (“MC”) cable provide electrical wiring in various types of construction applications. The type, use and composition of these cables must satisfy certain standards as set forth, for example, in the National Electric Codes (NEC®). These cables house electrical conductors within a metal armor. The metal armor may be flexible enabling the cable to bend while protecting the conductors against external damage during and after installation. The armor which houses the electrical conductors may be made from steel or aluminum. Typically, the metal armor sheath is formed from strip steel, for example, which is helically wrapped to form a series of interlocked “S” shaped sections along a longitudinal length of the cable.
Generally, AC and MC cable have different internal constructions and performance characteristics and are governed by different standards. For example, MC cable is manufactured according to UL standard 1569 and includes a conductor assembly with no limit on the number of electrical conductors having a particular AWG (American Wire Gauge). The conductor assembly may contain a grounding conductor. The electrical conductors and the ground conductor are cabled together in a left or right hand lay, but must end in a left hand lay. The conductors are encased collectively in an overall covering. In particular, MC cable includes either a covering over all of the electrically insulated conductors and the grounding conductor after cabling or a covering over just the electrical insulated conductors combined after cabling while the grounding conductor is positioned externally separate from this overall covering. The assembly is then fed into an armoring machine where metal tape is helically applied around the assembly to form a metal sheath. The metallic sheath of MC cable may be used as an equipment grounding conductor if the ohmic resistance satisfies the requirements of UL 1569. A grounding/bonding conductor may be included which, in combination with the metallic sheath, satisfies the UL ohmic resistance requirement. In this case, the metallic sheath and the grounding/bonding conductor would compose what is referred to as a metallic sheath assembly.
In contrast, AC cable is manufactured to UL Standard 4 in accordance with Section 320 of the National Electrical Code NEC® and can only contain up to four (4) insulated conductors (copper, aluminum, etc.) which are cabled together in a left hand lay as per Section 5.5 of UL Standard 4. Each electrical conductor is covered with a thermoplastic insulation and a jacket layer which are individually wrapped in a fibrous material. Similar to MC cable, the electrical conductors are disposed within a metal armor or sheath. If a grounding conductor is employed in AC cables, the grounding conductor is either (i) separately covered or wrapped with the fibrous material before being cabled for thermoplastic insulated conductors; or (ii) enclosed in the fibrous material together with the insulated conductors for thermoset insulated conductors. In either configuration, the bare grounding conductor is prevented from contacting the metal armor by the fibrous material. Additionally in AC type cable, a bonding strip or wire is laid lengthwise longitudinally (not cabled) along the conductors and is in intimate contact with the metal armor or sheath providing a low-impedance fault return path to safely conduct fault current.
The bonding strip for AC cable is composed of a minimum 16 AWG aluminum strip or wire. The bonding strip is unique to AC cable and allows the outer metal armor or sheath in conjunction with the bonding strip to provide a low impedance equipment grounding path. NEC® Section 320-104 provides that each electrically insulated conductor in an AC cable is covered with an overall moisture-resistant and fire-retardant fibrous material and if a grounding conductor is used, the fibrous material is disposed between the ground wire and the metal armored sheath. This provides that the ground conductor is separate from the bonding strip and allows the bonding strip to be in electrical contact with the interior surface of the metal sheath to provide the low impedance equipment grounding path. However, the fibrous material used to wrap each circuit conductor and ground conductor requires additional time and manpower during use and installation. In particular, an installer must first unwrap the fibrous material to expose the insulation/jacket before cutting the conductors required to complete a desired connection. In addition, the fibrous material may be subject to decomposition which may compromise the mechanical protection of the cable. Although the fibrous material may provide some moisture resistance and may be flame retardant, it may not provide a sufficient level of these properties for a particular application and/or location. Moreover, if moisture does penetrate into the fibrous material, the moisture will not wick away thereby potentially compromising the cable. Thus, there is a need for an improved AC cable that overcomes the drawbacks of the prior art.